1. Field of the Invention
The present invention pertains to cryogenic freezers, and in particular to tunnel freezers wherein a conveyor belt carrying product passes through an elongated tunnel-shaped freezer, with frozen, partially frozen, or cooled product emerging at the exit end of the freezer.
2. Description of the Related Art
Improvements have been sought for so-called cryogenic tunnel freezers, especially such freezers employing carbon dioxide "snow" as a cooling media. Although a variety of different fan configurations have been employed within the tunnel freezers for distributing the carbon dioxide snow, difficulties have been encountered from time to time in operating prior art freezers, especially at high cryogen input levels over long periods of time. It is particularly desirable that the environment within a tunnel freezer be isolated from the ambient to avoid adding to the heat and moisture loads carried by product being processed, (i.e., chilled or frozen) by the freezer apparatus. After prolonged operation, significant quantities of carbon dioxide snow are generated in the freezer interior. Fans within the freezer are provided to circulate the carbon dioxide snow, but over time, increasing amounts of carbon dioxide snow come out of circulation, becoming trapped within various parts of the freezer interior. If excessive amounts of snow or liquid are allowed to accumulate in the freezer interior circulation may be reduced, and free movement of equipment within the freezer may become impaired. Given the substantial amount of down time which may be required to service a freezer during a prolonged production run, further improvements in freezer performance are being sought.